Synaptic dysfunction in Parkinson’s disease

1Barbara Picconi,

2Giovanni Piccoli and

1,3Paolo Calabresi

1Laboratorio di Neurofisiologia, Fondazione Santa Lucia, I.R.C.C.S., 00143, Rome, Italy

2Consiglio Nazionale delle Ricerche Institute of Neuroscience, Milano, Italy.

3Clinica Neurologica, Università di Perugia, Ospedale S. Maria della Misericordia, 06156, Perugia,

Italy

Corresponding author:

Professor Paolo Calabresi

Clinica Neurologica, Facoltà di Medicina e Chirurgia

Università degli Studi di Perugia, Ospedale S. Maria della Misericordia

06156 Perugia - Italy

Tel +39 (0) 75 5784230 FAX +39 (0) 755784229

E mail calabre@unipg.it

Running head: Synaptic changes in PD

2

Abstract

Activity-dependent modifications in synaptic efficacy such as long term depression (LTD) and long

term potentiation (LTP), represent key cellular substrates for adaptive motor control and procedural

memory. The impairment of this two form of synaptic plasticity in the nucleus striatum could

account for the onset and the progression of motor and cognitive symptoms of Parkinson’s disease

(PD), characterized by the massive degeneration of dopaminergic neurons. In fact, both LTD and

LTP are peculiarly controlled and modulated by dopaminergic transmission coming from

nigrostriatal terminals.

Changes in corticostriatal and nigrostriatal neuronal excitability may influence profoundly the

threshold for the induction of synaptic plasticity, and changes in striatal synaptic transmission

efficacy are supposed play a role in the occurrence of PD symptoms. Understanding of these

maladaptive forms of synaptic plasticity has mostly come from the analysis of experimental animal

models of PD. A series of cellular and synaptic alterations occur in the striatum of experimental

parkinsonism in response to the massive dopaminergic loss. In particular, dysfunctions in

trafficking and subunit composition of glutamatergic NMDA receptors on striatal efferent neurons

contribute to the clinical features of the experimental parkinsonism.

Interestingly, it has become increasingly evident that in striatal spiny neurons the correct assembly

of NMDA receptor complex at the postsynaptic site is a major player in early phases of PD and it is

sensitive to distinct degrees of DA denervation. The molecular defects at the basis of PD

progression may be not confined just at the postsynaptic neuron: accumulating evidences have

recently shown that the genes linked to PD play a critical role at the presynaptic site. DA release

into the synaptic cleft relies on a proper presynaptic vesicular transport: impairment of SV

trafficking, modification of DA flow and altered presynaptic plasticity has been described in several

PD animal models. Furthermore, an impaired DA turnover has been described in presymptomatic

PD patients. Thus, given the pathological events occurring precociously at the synapses of PD

3

patients, post and presynaptic site may represent an adequate target for early therapeutic

intervention.

Introduction

Parkinson’s disease (PD) is one of the most frequent human neurodegenerative disorders associated

with the process of cerebral aging. PD physiopathology is linked to a widespread process of

degeneration of dopamine (DA) secreting-neurons in the Substantia Nigra pars compacta (SNc),

with the consequent loss of the neurons projecting to the striatum (Lang and Lozano, 1998a,b). The

parkinsonian symptoms appear when brain levels of DA reach the 70%-80% of the normal levels.

The main clinical features of PD are the direct consequences of a dysfunction occurring within both

the striatum and the entire basal ganglia system (Calabresi et al. 2007). Bradykinesia, rigidity,

tremor at rest, postural instability, micrographia and shuffling gait represent the principal motor

symptoms that allow the diagnosis of PD (Jankovic, 2008). The clinical detection of these motor

symptoms is often accompanied by autonomic, cognitive and psychiatric problems (Calabresi et al.

2006; Kehagia et al. 2010). Rare forms of PD resulted from missense mutations of α-synuclein as

well as increased expression of normal α-synuclein, are characterized by early-onset and autosomal

dominant inheritance (Polymeropoulos et al. 1997; Singleton et al. 2003). Intracytoplasmic

inclusions called Lewy bodies and the progressive loss of DA-containing neurons in the SNc

represent the main neuropathological features of the genetic forms of PD (Spillantini et al. 1998;

Dickson et al. 2009; Schulz-Schaeffer, 2010).

Mutations in seven genes have been implicated in various forms of familiar parkinsonism. Two

autosomal-dominant genes (α-synuclein and LRRK2) and three autosomal-recessive genes (parkin,

DJ-1 and PINK1) have been definitively associated with inherited PD (Nussbaum and

Polymeropoulos, 1997; Polymeropoulos et al. 1997; Healy et al. 2004; Paisan-Ruiz et al. 2004;

Valente et al. 2004). As well as these, other mutations have been reported in UCHL-1, synphilin-1

and NR4A2 that may or may not be biologically significant (Leroy et al. 1998; Le et al. 2003; Marx

4

et al. 2003). Synaptic loss is one of the major neurobiological dysfunction occurring in several

neurological diseases (Wishart et al. 2006); for example synaptic failure happens in a very early

phase in both patients and animal models during the progression of Alzheimer’s disease (Selkoe,

2002).

Parkinson’ s disease and presynaptic dysfunction

Accumulating evidence has convincingly demonstrated that the genes linked to PD play a critical

role at the presynaptic site. α-synuclein is a 140-aminoacid protein, present in almost all sub-

cellular compartments, but particularly enriched in the presynaptic terminals where it is loosely

associated with the distal reserve pool of synaptic vesicles (Lavedan, 1998; Yu et al. 2007).

Structural and functional studies have shown that α-synuclein is involved in the trafficking of

synaptic vesicles. In fact, the presynaptic boutons of cultures lacking α-synuclein presented a

marked reduction in the number of vesicles present in the distal pool although the number of

vesicles docked at the synaptic plasma remained unaltered (Murphy et al. 2000). Accordingly, α-

synuclein knockout (KO) mice showed a marked decrease in the pool of undocked synaptic vesicles

and significantly impaired hippocampal response to long-lasting low frequency stimulation (Cabin

et al. 2002). Furthermore, α-synuclein KO mice are characterized by an increased evoked DA

release: these observations might imply that α-synuclein normally acts as a negative regulator of

DA neurotransmission in an activity-dependent fashion (Abeliovich et al. 2000). Strikingly, over-

expression of α-synuclein inhibits neurotransmitter release affecting specifically the size of the

synaptic vesicle recycling pool (Nemani et al. 2010). Thus, α-synuclein seems to be deeply

implicated in the synaptic vesicle trafficking required for a proper presynaptic DA release by

keeping low the amount of DA within the presynaptic bouton (Sidhu et al. 2004; Yu et al. 2005).

Given that cytosolic DA might be converted into highly reactive oxidative molecules, it can be

speculated that pathological mutations or aggregation of α-synuclein might prejudice normal α-

5

synuclein functions. This impairment may bring to accumulation of DA and thus to the generation

of toxic moieties. Interestingly, also DJ-1 and PINK1 KO mice exhibit presynaptic defects. DJ-1 is

a redox-sensitive molecular chaperone and it has been proposed that it inhibits protein aggregation,

including α-synuclein formations (Shendelman et al. 2004; Wilson et al. 2004; Moore et al. 2006;

Gasser, 2009). DJ-1 is expressed widely throughout the tissues and it is sub-cellularly localized to

the cytosol, mitochondrial matrix and intermembrane space (Zhang et al. 2005). Acute slice

preparation from DJ-1 KO mice showed a reduce DA overflow and impaired LTD. Furthermore

the mice had a poor performance in terms of spontaneous activities and generalized hypokinesia in

open field (Goldberg et al. 2003, 2005). DJ-1 has been reported to sustain also hippocampal LTD

consolidation, suggesting a potential involvement for this protein in modulating hippocampal

dependent cognitive dysfunctions reported in PD (Wang et al. 2008). PINK1 instead is a

serine/threonine kinase localized in the mitochondria (Silvestri et al. 2005; Zhou et al. 2008). If

PINK1 KO mice failed to exhibit any major abnormality, they showed clear deficits in nigrostriatal

DA neurotransmission. Robust evidence supports the conclusion that loss of PINK1 function causes

a selective impairment in exocytotic DA release (Kitada et al. 2007; Gispert et al. 2009). Actual

knowledge about PINK1 suggests that it may resides in the mitochondria but, given that its kinase

domain faces the cytosol, it may have extra-mitochondrial phospho-targets (Silvestri et al. 2005).

Therefore, it might be argued that PINK1 can modify via phosphorylation the activity of proteins

involved in DA release. Noteworthy, it has been demonstrated that Parkin, PINK1, and DJ-1

interact physically and functionally. In fact, these three proteins form a ternary complex that

promotes ubiquitination and degradation of aberrantly expressed and heat shock–induced Parkin

substrates, as Parkin itself and Synphilin-1. Pathogenic mutants might reduce the activity of the

degradative complex (Xiong et al. 2009).

Mutations in LRRK2 gene account for up to 13% of familial PD cases compatible with dominant

inheritance (Paisan-Ruiz et al. 2004, 2008; Zimprich et al. 2004) and 1 to 2% of sporadic PD

patients, thus suggesting this protein as the most significant player in PD pathogenesis identified to

6

date (Aasly et al. 2005; Berg et al. 2005; Taylor et al. 2006). Clinically and pathologically, the

features of LRRK2-associated parkinsonism are often indistinguishable from idiopathic PD;

although pathologic variability exists even within PARK8-linked kindred, ranging from nigral

neuronal loss only, to general neuronal loss with α-synuclein, ubiquitin or tau inclusions [reviewed

in (Whaley et al. 2006)]. Furthermore, the neuropathology demonstrated in post-mortem brain

examinations of patients with LRRK2 mutations most often involves synucleinopathy, but

occasionally tauopathy, suggesting a role for LRRK2 that is upstream of protein inclusion

pathology (Zimprich et al. 2004; Taymans and Cookson, 2010; Wider et al. 2010). The LRRK2

protein has a molecular weight of approximately 280 kDa and contains several domains including a

Ras/GTPase like (Roc), a C-terminal of Roc (COR), a kinase (similar to mitogen activated protein

kinase kinase kinases) and a WD40 domain (Bosgraaf and Van Haastert, 2003; Guo et al. 2006).

Phylogenetically the LRRK2 kinase domain belongs to the TKL (tyrosine like kinases) and shows

high similarity to Mixed lineage kinases (MLKs) (Manning et al. 2002; Marin, 2006). Few LRRK2

substrates, including moesin, 4E-BP, MKKs, tubulin beta, and α-synuclein have been found so far

in in vitro assays (Jaleel et al. 2007; Imai et al. 2008; Gillardon, 2009; Gloeckner et al. 2009; Qing

et al. 2009). Several single nucleotide alterations have been identified in LRRK2 (Lesage et al.

2005; Mata et al. 2005), covering all functional domains, but only five missense mutations clearly

segregate with PD in large family studies (Goldwurm et al. 2005; Bonifati, 2006a,b). Disease

segregating mutations in LRRK2 have been reported in the kinase domain (G2019S, I2020T), the

Roc domain (R1441C/G) and in the COR domain (Y1699C) [reviewed in (Mata et al. 2005)].

The most common mutation found in western countries kindred, G2019S, falls in the kinase domain

and increases LRRK2 kinase activity while mutations in the Roc domain appear to decrease the

GTPase activity of LRRK2, to affect protein dimerization and to slightly increase kinase activity

[reviewed in more detail in (Moore, 2008)]. The G2019S mutation have been identified also in

Parkinsonism patients with no family history of disease (Gilks et al. 2005; Healy et al. 2008); other

LRRK2 variants affecting kinase activity appear to be important risk factors in two genome wide

7

association studies of sporadic PD (Simon-Sanchez et al. 2009). Although studies show little

concordance regarding the level of LRRK2 mRNA/protein expression in the SN, LRRK2 protein

expression has been demonstrated in tyrosine-hydroxylase positive neurons of the SNc and in

medium–sized spiny neurons of the striatum (Galter et al. 2006; Melrose et al. 2006; Higashi et al.

2007a,b). Cortical regions that are affected in dementia associated with PD, including pyramidal

neurons of the cerebral cortex and of Ammon’s horn, also demonstrate relatively high levels of

LRRK2 (Biskup et al. 2006; Higashi et al. 2007b). At the sub-cellular level, precedent studies

showed LRRK2 is mainly associated with mitochondria but also with multiple vesicles structure,

including synaptic vesicles (Biskup et al. 2006). Despite its predominance in PD, the physiological

function of LRRK2 is not known, and therefore its precise role in the aetiology of PD is far from

being understood.

Neurotransmission defects have been repeatedly observed in different LRRK2 models (Li et al.

2009; Tong et al. 2009; Xiong et al. 2009; Li et al. 2010). Functional impairments in nigrostriatal

dopaminergic innervation and degeneration of the nigrostriatal projections have been demonstrated

in R1441C-LRRK2 homozygous knock-in mice (Tong et al. 2009) and in R1441C-LRRK2 BAC

transgenic mice (Li et al. 2009), respectively. G2019S BAC transgenic mice show deficiencies in

striatal dopamine release and enhanced striatal tau immunoreactivity without dopaminergic neuron

loss in the substantia nigra (Li et al. 2010). Recent studies have enlightened that LRRK2 acts

directly at the secretory and endocytic molecular machinery (Shin et al., 2008; Xiong et al. 2010).

Finally, it has been shown that electrophysiological properties as well as proper vesicular trafficking

and spatial distribution in the presynaptic pool depend on the presence of LRRK2 as an integral part

of presynaptic protein complex (Piccoli et al. 2011). Presynaptic proteins – NSF, AP-2 complex

subunits, SV2A, synapsin , syntaxin 1 (Piccoli et al. 2011) and Rab5b (Shin et al. 2008)- as well as

actin (Meixner et al. 2010) have been found to interacts, at least in vitro, with LRRK2. These

proteins have been previously described as key elements of synaptic vesicle trafficking. NSF

catalyzes the release of the SNARE complex (SNAP 25, syntaxin 1 and VAMP) and allows the first

8

step of the endocytic cycle where also Rab5 proteins are called in action. The clathrin complex

[clathrin, AP-2 adaptor complex and accessories protein as dynamin and AP180] constitutes one of

the major pathways for SV recycling from the membrane to the resting pool (RP). The control of

storage and mobilization of SV in the RRP depends instead on the synaptic vesicle glycoproteins

SV2A and B while synapsins are thought to immobilize SV in the RP by cross-linking vesicles to

the actin cytoskeleton. Strikingly, an increased DA turnover has been noticed in presymptomatic

LRRK2 mutation carriers (Sossi et al. 2010). Increased turnover might arise as a compensatory

mechanism to counteract DA-neurons loss (Adams et al. 2005), but it has also been suggested that

increased DA turnover might by itself contribute to disease progression secondary to DA-associated

toxicity (Smith et al. 2002; Zigmond et al. 2002). Therefore, accumulating evidences suggest that

synaptic dysfunction is a primary effect of LRRK2 gene mutations and that synaptic failure is

intimately involved in LRRK2 due PD pathogenesis.

Postsynaptic dysfunction in Parkinson’s disease

The natural history of PD is complex and involves differential mechanisms during its various

clinical phases. Most of the evidence on pathogenic pathways in PD has been obtained using

experimental models of complete striatal DA depletion mimicking advanced PD such as rats

lesioned with 6-hydroxydopamine (6-OHDA) (Schwarting and Huston, 1996) and macaques

lesioned with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (Jenner and Marsden, 1986).

The massive denervation of the dopaminergic nigrostriatal terminals, as observed in advanced PD,

is associated to maladaptive plasticity (Calabresi et al. 2007), alteration of striatal dendritic spines

(Anglade et al. 1996; Day et al. 2006), and changes of glutamatergic signaling (Betarbet et al. 2000;

Picconi et al. 2004). In advanced PD spontaneous excitatory glutamatergic synaptic activity can be

dramatically altered. These pathological events may also alter the amplitude and the direction of

long-term changes of excitatory transmission induced by repetitive synaptic activation. Moreover,

changes in neuronal phasic and/or tonic firing discharge may occur. Even slight changes in

9

corticostriatal and nigrostriatal neuronal excitability may influence profoundly the threshold for the

induction of synaptic plasticity. Changes in striatal synaptic transmission efficacy are supposed to

be the cellular basis for such complex integrative functions (Calabresi et al. 2006, 2007) and

experimental findings show that short- and long-term changes in corticostriatal synaptic plasticity

may play a role in PD (Gubellini et al. 2002; Picconi et al. 2003).

Two cardinal features of PD pathophysiology are represented by the alteration of glutamatergic

synapses paradoxically accompanied by the described increase of glutamatergic transmission within

the striatum. The real mechanisms underlying this increased excitatory drive remains unknown.

Recently, the synaptic changes in both corticostriatal and thalamostriatal afferents have been

studied in MPTP-treated monkeys taking as main markers the vesicular glutamate transporters

(vGluTs) 1 and 2 (Raju et al. 2008). This study demonstrates the increased presence of vGluT1 in

the striatum of MPTP monkeys without any significant change in the pattern of synaptic

connectivity. However, a clear degree of synaptic reorganization of the thalamostriatal system has

been found. These findings suggest a differential degree of plasticity between the two systems in

parkinsonian primates.

In the last decades have been described and extensively studied two forms of striatal synaptic

plasticity (long-term depression (LTD) and long-term potentiation (LTP)) thought to underlie

cognitive performance both in vitro (Calabresi et al. 1992b,c; Lovinger et al. 1993; Walsh, 1993;

Walsh and Dunia, 1993; Partridge et al. 2000) and in vivo (Charpier and Deniau, 1997; Reynolds

and Wickens, 2000; Mahon et al. 2004).

A high frequency stimulation (HFS) protocol of the corticostriatal fibers (Calabresi et al. 1992b,c;

Lovinger et al. 1993) allows to induce both form of synaptic plasticity, being the type of the long-

lasting changes critically dependent upon the level of membrane depolarization and on the

ionotropic glutamate receptor subtype activated during the HFS. A third form of synaptic plasticity

(depotentiation) results from the reversal of an established LTP by the application of a low-

frequency stimulation of corticostriatal fibers (O'Dell and Kandel, 1994; Picconi et al. 2003).

10

Compared to other brain areas, in which synaptic plasticity has been extensively studied, the

striatum has the peculiar feature of receiving a massive dopaminergic input arising from SNc.

Accordingly, a unique characteristic of striatal LTD is the requirement of DA receptor activation by

endogenous DA (Calabresi et al. 2007). In fact, this form of synaptic plasticity is lost after massive

DA denervation both in 6-OHDA rats (Calabresi et al. 1992c) and MPTP-treated monkeys (Quik et

al. 2006).

The absence of LTD in the striatum of parkinsonian animals can be attributed to the failed

activation of DA receptors during the induction phase of this form of synaptic plasticity. LTD, in

fact, can be restored after DA denervation by ensuring DA receptor activation through the

application of exogenous DA, or by the co-activation of both D1 and D2 receptors (Calabresi et al.

1992a, 2007). Similarly, massive nigrostriatal denervation blocks corticostriatal LTP (Picconi et al.

2003; Calabresi et al. 2007). Interestingly, a "balanced" DA/DARPP-32 pathway is required for the

corticostriatal system to be able to express both LTD and LTP (Calabresi et al. 2000).

It is of interest to note that distinct degrees of DA denervation may differentially affect the

induction and maintenance of these two distinct and opposite forms of corticostriatal synaptic

changes (Paille et al. 2010). An incomplete DA denervation does not affect corticostriatal LTD

which is, however, abolished by a complete lesion suggesting that a low, although critical, level of

DA is required for this form of synaptic plasticity. Conversely, an incomplete DA denervation

dramatically alters the maintenance of LTP confirming a critical role of this form of synaptic

plasticity in the early motor parkinsonian symptoms (Paille et al. 2010).

Recently, to understand the early synaptic mechanisms occurring in PD the striatal dysfunctions

have been studied in mice overexpressing human A53T-alfa-synuclein (Kurz et al. 2010). A53T-

alfa-synuclein over-expressing mice, in their advanced stage, present dysfunctional DA

neurotransmission and consequently an impaired striatal LTD. Confirming, once more, the relevant

role of an intact and correct balance in the dopaminergic nigrostriatal transmission for a

physiological synaptic activity.

11

The pathophysiological picture emerging from the last years of experimental approach shows that

the strength of glutamatergic signals from the cortex to the striatum might be dynamically regulated

during the progression of the disease. In fact, bidirectional changes in corticostriatal synaptic

plasticity are critically controlled by the different degree of nigral denervation which influences the

endogenous DA levels and the assembly of striatal N-methyl-D-aspartate (NMDA) type glutamate

receptor subunits.

NMDA receptors are glutamate ion channels, and represent the key elements in the regulation of

synaptic function in the central nervous system. They resulted from the co-assembly of three

different receptor subunit families: NMDA receptor 1 (NR1), NR2A-NR2D and NR3A-NR3B

(Dingledine et al. 1999; Nishi et al. 2001). NMDA receptors are highly permeable to Ca2+

, and its

influx through the receptor channel is essential for the synaptogenesis, the synaptic remodeling and

the long-lasting changes in synaptic efficacy such as synaptic plasticity (Collingridge et al. 2004).

In the neuronal synapses, NMDA receptors are clustered in the postsynaptic density (PSD) that

consists of numerous scaffolding cytoskeletal and signaling proteins, some of which are in close

contact with the cytoplasmic domain of glutamate ionotropic receptors in the postsynaptic

membrane (Kennedy, 2000; Gardoni et al. 2001). This accumulation of NMDA receptors at the post

synaptic compartment ensures a rapid response to neurotransmitter release and provides a molecular

mechanism for linking the transmembrane ion flux to the signaling machinery responsible for

specific second messenger pathways. Among the proteins complex governing the response of the

signaling cascade the α-calcium-calmodulin-dependent protein kinase II (α-CaMKII) is directly

linked to the NR2A/NR2B subunits (Gardoni et al. 1998; Strack et al. 2000) and competes in NR2A

binding with PSD-95 (Gardoni et al. 2001). Interestingly, CaMKII- and tyrosine-dependent

phosphorylation of NMDA receptors are altered in experimental model of PD (Oh et al. 1999).

In the striatum as well as in other brain areas LTP requires activation of NMDA receptors

(Calabresi et al. 1992b, 2007; Collingridge and Bliss, 1995; Malenka and Bear, 2004). Interestingly,

12

it has become increasingly evident that in striatal spiny neurons NMDA receptor complex is also

profoundly altered in experimental PD (Ulas and Cotman, 1996; Dunah and Standaert, 2001).

Early studies evaluated NMDA receptor abundance, composition, and phosphorylation in advanced

model of PD. In the DA denervated striatum has been found a decreased level of NR1 and NR2B

subunits in striatal membranes, while the abundance of NR2A was unchanged (Ulas and Cotman,

1996; Dunah and Standaert, 2001). Further studies in the 6-OHDA model showed similar results

and associated to alterations in synaptic plasticity (Picconi et al. 2003, 2004; Gardoni et al. 2006).

In particular, NR2B subunit was specifically reduced in the synaptic density from advanced

parkinsonian rats when compared with sham-lesioned rats in the absence of parallel alterations of

NR1 and NR2A (Picconi et al. 2003, 2004; Gardoni et al. 2006). Interestingly, these molecular

alterations have been further confirmed in parkinsonian macaques (Hallett et al. 2005). Hallett’s

group shows that in the striatum of MPTP-lesioned macaques the DA depletion induces massive

changes in the levels of striatal NMDA receptor proteins, such as a reduction in the abundance of

NR1 and NR2B but not NR2A subunit. Moreover, in the denervated striatum of parkinsonian

animals the alteration of NMDA receptor subunit localization at synaptic sites is accompanied by a

decreased recruitment of PSD-95 to NR2A–NR2B subunits; these events are paralleled by an

increased activation of the pool of α-CaMKII associated to the NMDA receptor complex (Picconi et

al., 2004). Further, other studies reported that experimental parkinsonism in rats appears to be

associated with decreased synaptic membrane localization and increased vesicular localization of

PSD-95 and SAP97 members of the PSD-MAGUK family (Nash et al. 2005) that could account for

dysregulation of NMDA receptors at synapses.

While in advanced parkinsonism LTP is completely lost and this synaptic alteration is coupled to

specifically reduced levels of NR2B subunits in the PSD compartment (Gardoni et al. 2006), the

picture found in the early parkinsonian rats is quite different.

As mentioned above, the incomplete DA denervation dramatically alters the maintenance of LTP.

This synaptic alteration recorded in striatal spiny neurons is also accompanied by a dramatic

13

increase in the NR2A NMDA receptor subunits in the striatal synapses, suggesting the presence of a

profound rearrangement of the receptor complex composition (Paille et al. 2010). These profound

differences in NMDA receptors in the postsynaptic compartment of partially versus fully lesioned

rats suggest that NR2-type regulatory subunits are sensitive to plastic changes induced by the

differential degree of DA denervation.

Moreover, NMDA receptor subunits NR2A and NR2B interact with membrane-associated

guanylate kinases (MAGUK); this interaction governs their trafficking and clustering at synaptic

sites (Kim and Sheng, 2004). The analysis of PSD-95, SAP97, and SAP102 in the postsynaptic

compartment reveals a significant reduction of the three proteins in advanced parkinsonian rats

compared with sham-operated rats (Gardoni et al. 2006). In contrast, in early parkinsonian animals

the level of these proteins is the same as in the sham-operated animals suggesting that in this model

of “early” PD no alteration of MAGUK protein distribution at the synapse is present. These data

suggest that the NR2A subunit level at the synaptic site is a major player in early phases of PD and

it is sensitive to distinct degrees of DA denervation; thus, it may represent an adequate target for

early therapeutic intervention.

In the PSD another important receptors included in the glutamatergic ionotropic receptors class, and

mediating the functions of glutamate, are represented by alpha-amino-3-hydroxy-5-methyl-4-

isoxazolepropionic acid (AMPA) receptors, tetrameric proteins composed of subunits GluR1-4.

Upon binding with glutamate, synaptic AMPA receptors induce membrane depolarization and after

removing magnesium (Mg2+

) block from NMDA, allow to reduce the threshold to induce long-term

increases of the synaptic responses. AMPA receptor-dependent depolarization also open L-type

Calcium (Ca2+

) channels and lead to activation of CRE elements that are responsible for gene

transcription.

Recently, has been shown a critical role of AMPA receptors in PD (Lee et al. 2008). Lee and

colleagues found that paraquat, a putative causative agent for PD, inhibits postsynaptic AMPA

receptors on dopaminergic neurons in the SNc. However, there is still no general consensus on the

14

mechanism underlying dysregulation of AMPA receptor distribution or composition changes in PD.

GluR1 subunit of AMPA receptor has not found changed in the striatum of parkinsonian rats

(Bernard et al. 1996; Betarbet et al. 2000) while GluR1 immunoreactivity is increased in the

caudate and putamen of MPTP monkeys (Betarbet et al. 2000). Evidence has been provided that

GluR1 immunoreactivity is decreased in striatal spiny neurons (Lai et al. 2003) and in striatal

membrane fractions of parkinsonian rats (Gardoni et al. 2006); on the contrary, no alteration of

GluR1 levels in the post synaptic density has been found in 6-OHDA-lesioned rats (Picconi et al.

2004).

Conclusions

Given the correlation recently described between LRRK2 and α-synuclein (Lin et al. 2009

Carballo-Carbajal et al. 2010), the impact of α-synuclein on synaptic vesicle recycling (Fortin et al.

2010; Nemani et al. 2010) and the functional links among DJ-1, Parkin, PINK1 and α-synuclein

(Shendelman et al. 2004; Xiong et al. 2009), the regulation of DA release might arise as one the

main biological pathway compromised during PD onset. The molecular mechanisms underlying

these synaptic transmission defects, however, remain largely elusive. Although little is known about

the precise mechanisms of exocytotic DA release, it likely uses a similar mechanism as

glutamatergic synapses, in which release is energy-dependent, is mediated by the SNARE-

dependent fusion of synaptic vesicles, and is triggered by Ca2+

binding to synaptotagmins. Synaptic

vesicles undergo in the nerve terminal to high frequency trafficking cycles thanks to the presence of

extremely specialized machinery, allowing very rapid triggering and switching off of synaptic

vesicle exocytosis in response to depolarization-evoked Ca2+

influx. A major goal in neurobiology

in recent years has been to gain insight into the molecular machinery that mediates neurotransmitter

release. More than 1000 proteins function in the presynaptic nerve terminal, and hundreds are

thought to participate in exo-endocytosis. The processes is finely tuned and depends on the

15

interaction between protein expressed on SV membranes and protein expressed on the presynaptic

membranes (Rizo and Rosenmund, 2008; Sudhof and Rothman, 2009).

This complex network of interaction is plastically shaped by post-translational modifications: the

presynaptic modulation of neurotransmitter release is in fact altered by protein kinases and protein

phosphatases (Turner et al. 1999; Fdez and Hilfiker, 2006) and by protein degradation (Ehlers,

2003; Yao et al. 2007). One possibility worth to be explored is that PD- related proteins alter SV

trafficking via modification of presynaptic proteins.

Cellular and postsynaptic alterations occurring in the striatum of experimental parkinsonism in

response to the massive dopaminergic loss may lead to synaptic dysfunction and corticostriatal

transmission instabilities. In particular, maladaptive forms of synaptic plasticity consequently to the

alteration in the subunit composition of glutamatergic ionotropic receptors, i.e. NMDA receptors,

contribute to the clinical features PD. Interestingly, it has become increasingly evident that the

correct assembly of NMDA receptor complex at the synaptic site is a major player in early phases

of PD and it is sensitive to distinct degrees of DA denervation; thus, it may represent an adequate

target for early therapeutic intervention.

References

1. Aasly JO, Toft M, Fernandez-Mata I, Kachergus J, Hulihan M, White LR, Farrer M (2005)

Clinical features of LRRK2-associated Parkinson's disease in central Norway. Ann Neurol

57: 762-765.

2. Abeliovich A, Schmitz Y, Farinas I, Choi-Lundberg D, Ho WH, Castillo PE, Shinsky N,

Verdugo JM, Armanini M, Ryan A, Hynes M, Phillips H, Sulzer D, Rosenthal A (2000)

Mice lacking alpha-synuclein display functional deficits in the nigrostriatal dopamine

system. Neuron 25: 239-252.

3. Adams JR, van Netten H, Schulzer M, Mak E, McKenzie J, Strongosky A, Sossi V, Ruth

TJ, Lee CS, Farrer M, Gasser T, Uitti RJ, Calne DB, Wszolek ZK, Stoessl AJ (2005) PET in

LRRK2 mutations: comparison to sporadic Parkinson's disease and evidence for

presymptomatic compensation. Brain 128: 2777-2785.

16

4. Anglade P, Mouatt-Prigent A, Agid Y, Hirsch E (1996) Synaptic plasticity in the caudate

nucleus of patients with Parkinson's disease. Neurodegeneration 5: 121-128.

5. Berg D, Schweitzer K, Leitner P, Zimprich A, Lichtner P, Belcredi P, Brussel T, Schulte C,

Maass S, Nagele T (2005) Type and frequency of mutations in the LRRK2 gene in familial

and sporadic Parkinson's disease*. Brain 128: 3000-3011.

6. Bernard V, Gardiol A, Faucheux B, Bloch B, Agid Y, Hirsch EC (1996) Expression of

glutamate receptors in the human and rat basal ganglia: effect of the dopaminergic

denervation on AMPA receptor gene expression in the striatopallidal complex in Parkinson's

disease and rat with 6-OHDA lesion. J Comp Neurol 368: 553-568.

7. Betarbet R, Porter RH, Greenamyre JT (2000) GluR1 glutamate receptor subunit is

regulated differentially in the primate basal ganglia following nigrostriatal dopamine

denervation. J Neurochem 74: 1166-1174.

8. Biskup S, Moore DJ, Celsi F, Higashi S, West AB, Andrabi SA, Kurkinen K, Yu SW, Savitt

JM, Waldvogel HJ, Faull RL, Emson PC, Torp R, Ottersen OP, Dawson TM, Dawson VL

(2006) Localization of LRRK2 to membranous and vesicular structures in mammalian brain.

Ann Neurol 60: 557-569.

9. Bonifati V (2006a) Parkinson's disease: the LRRK2-G2019S mutation: opening a novel era

in Parkinson's disease genetics. Eur J Hum Genet 14: 1061-1062.

10. Bonifati V (2006b) The pleomorphic pathology of inherited Parkinson's disease: lessons

from LRRK2. Curr Neurol Neurosci Rep 6: 355-357.

11. Bosgraaf L, Van Haastert PJ (2003) Roc, a Ras/GTPase domain in complex proteins.

Biochim Biophys Acta 1643: 5-10.

12. Cabin DE, Shimazu K, Murphy D, Cole NB, Gottschalk W, McIlwain KL, Orrison B, Chen

A, Ellis CE, Paylor R, Lu B, Nussbaum RL (2002) Synaptic vesicle depletion correlates

with attenuated synaptic responses to prolonged repetitive stimulation in mice lacking alpha-

synuclein. J Neurosci 22: 8797-8807.

13. Calabresi P, Maj R, Mercuri NB, Bernardi G (1992a) Coactivation of D1 and D2 dopamine

receptors is required for long-term synaptic depression in the striatum. Neurosci Lett 142:

95-99.

14. Calabresi P, Pisani A, Mercuri NB, Bernardi G (1992b) Long-term Potentiation in the

Striatum is Unmasked by Removing the Voltage-dependent Magnesium Block of NMDA

Receptor Channels. Eur J Neurosci 4: 929-935.

17

15. Calabresi P, Picconi B, Parnetti L, Di Filippo M (2006) A convergent model for cognitive

dysfunctions in Parkinson's disease: the critical dopamine-acetylcholine synaptic balance.

Lancet Neurol 5: 974-983.

16. Calabresi P, Picconi B, Tozzi A, Di Filippo M (2007) Dopamine-mediated regulation of

corticostriatal synaptic plasticity. Trends Neurosci 30: 211-219.

17. Calabresi P, Maj R, Pisani A, Mercuri NB, Bernardi G (1992c) Long-term synaptic

depression in the striatum: physiological and pharmacological characterization. J Neurosci

12: 4224-4233.

18. Calabresi P, Gubellini P, Centonze D, Picconi B, Bernardi G, Chergui K, Svenningsson P,

Fienberg AA, Greengard P (2000) Dopamine and cAMP-regulated phosphoprotein 32 kDa

controls both striatal long-term depression and long-term potentiation, opposing forms of

synaptic plasticity. J Neurosci 20: 8443-8451.

19. Carballo-Carbajal I, Weber-Endress S, Rovelli G, Chan D, Wolozin B, Klein CL, Patenge

N, Gasser T, Kahle PJ (2010) Leucine-rich repeat kinase 2 induces alpha-synuclein

expression via the extracellular signal-regulated kinase pathway. Cell Signal 22: 821-827.

20. Charpier S, Deniau JM (1997) In vivo activity-dependent plasticity at cortico-striatal

connections: evidence for physiological long-term potentiation. Proc Natl Acad Sci U S A

94: 7036-7040.

21. Collingridge GL, Bliss TV (1995) Memories of NMDA receptors and LTP. Trends Neurosci

18: 54-56.

22. Collingridge GL, Isaac JT, Wang YT (2004) Receptor trafficking and synaptic plasticity.

Nat Rev Neurosci 5: 952-962.

23. Day M, Wang Z, Ding J, An X, Ingham CA, Shering AF, Wokosin D, Ilijic E, Sun Z,

Sampson AR, Mugnaini E, Deutch AY, Sesack SR, Arbuthnott GW, Surmeier DJ (2006)

Selective elimination of glutamatergic synapses on striatopallidal neurons in Parkinson

disease models. Nat Neurosci 9: 251-259.

24. Dickson DW, Braak H, Duda JE, Duyckaerts C, Gasser T, Halliday GM, Hardy J, Leverenz

JB, Del Tredici K, Wszolek ZK, Litvan I (2009) Neuropathological assessment of

Parkinson's disease: refining the diagnostic criteria. Lancet Neurol 8: 1150-1157.

25. Dingledine R, Borges K, Bowie D, Traynelis SF (1999) The glutamate receptor ion

channels. Pharmacol Rev 51: 7-61.

26. Dunah AW, Standaert DG (2001) Dopamine D1 receptor-dependent trafficking of striatal

NMDA glutamate receptors to the postsynaptic membrane. J Neurosci 21: 5546-5558.

18

27. Ehlers MD (2003) Activity level controls postsynaptic composition and signaling via the

ubiquitin-proteasome system. Nat Neurosci 6: 231-242.

28. Fdez E, Hilfiker S (2006) Vesicle pools and synapsins: new insights into old enigmas. Brain

Cell Biol 35: 107-115.

29. Fortin DL, Nemani VM, Nakamura K, Edwards RH (2010) The behavior of alpha-synuclein

in neurons. Mov Disord 25 Suppl 1: S21-26.

30. Galter D, Westerlund M, Carmine A, Lindqvist E, Sydow O, Olson L (2006) LRRK2

expression linked to dopamine-innervated areas. Ann Neurol 59: 714-719.

31. Gardoni F, Caputi A, Cimino M, Pastorino L, Cattabeni F, Di Luca M (1998)

Calcium/calmodulin-dependent protein kinase II is associated with NR2A/B subunits of

NMDA receptor in postsynaptic densities. J Neurochem 71: 1733-1741.

32. Gardoni F, Schrama LH, Kamal A, Gispen WH, Cattabeni F, Di Luca M (2001)

Hippocampal synaptic plasticity involves competition between Ca2+/calmodulin-dependent

protein kinase II and postsynaptic density 95 for binding to the NR2A subunit of the NMDA

receptor. J Neurosci 21: 1501-1509.

33. Gardoni F, Picconi B, Ghiglieri V, Polli F, Bagetta V, Bernardi G, Cattabeni F, Di Luca M,

Calabresi P (2006) A critical interaction between NR2B and MAGUK in L-DOPA induced

dyskinesia. J Neurosci 26: 2914-2922.

34. Gasser T (2009) Molecular pathogenesis of Parkinson disease: insights from genetic studies.

Expert Rev Mol Med 11: e22.

35. Gilks WP, Abou-Sleiman PM, Gandhi S, Jain S, Singleton A, Lees AJ, Shaw K, Bhatia KP,

Bonifati V, Quinn NP, Lynch J, Healy DG, Holton JL, Revesz T, Wood NW (2005) A

common LRRK2 mutation in idiopathic Parkinson's disease. Lancet 365: 415-416.

36. Gillardon F (2009) Leucine-rich repeat kinase 2 phosphorylates brain tubulin-beta isoforms

and modulates microtubule stability--a point of convergence in parkinsonian

neurodegeneration? J Neurochem 110: 1514-1522.

37. Gispert S, Ricciardi F, Kurz A, Azizov M, Hoepken HH, Becker D, Voos W, Leuner K,

Muller WE, Kudin AP, Kunz WS, Zimmermann A, Roeper J, Wenzel D, Jendrach M,

Garcia-Arencibia M, Fernandez-Ruiz J, Huber L, Rohrer H, Barrera M, Reichert AS, Rub U,

Chen A, Nussbaum RL, Auburger G (2009) Parkinson phenotype in aged PINK1-deficient

mice is accompanied by progressive mitochondrial dysfunction in absence of

neurodegeneration. PLoS One 4: e5777.

19

38. Gloeckner CJ, Schumacher A, Boldt K, Ueffing M (2009) The Parkinson disease-associated

protein kinase LRRK2 exhibits MAPKKK activity and phosphorylates MKK3/6 and

MKK4/7, in vitro. J Neurochem 109: 959-968.

39. Goldberg MS, Pisani A, Haburcak M, Vortherms TA, Kitada T, Costa C, Tong Y, Martella

G, Tscherter A, Martins A, Bernardi G, Roth BL, Pothos EN, Calabresi P, Shen J (2005)

Nigrostriatal dopaminergic deficits and hypokinesia caused by inactivation of the familial

Parkinsonism-linked gene DJ-1. Neuron 45: 489-496.

40. Goldberg MS, Fleming SM, Palacino JJ, Cepeda C, Lam HA, Bhatnagar A, Meloni EG, Wu

N, Ackerson LC, Klapstein GJ, Gajendiran M, Roth BL, Chesselet MF, Maidment NT,

Levine MS, Shen J (2003) Parkin-deficient mice exhibit nigrostriatal deficits but not loss of

dopaminergic neurons. J Biol Chem 278: 43628-43635.

41. Goldwurm S, Di Fonzo A, Simons EJ, Rohe CF, Zini M, Canesi M, Tesei S, Zecchinelli A,

Antonini A, Mariani C, Meucci N, Sacilotto G, Sironi F, Salani G, Ferreira J, Chien HF,

Fabrizio E, Vanacore N, Dalla Libera A, Stocchi F, Diroma C, Lamberti P, Sampaio C,

Meco G, Barbosa E, Bertoli-Avella AM, Breedveld GJ, Oostra BA, Pezzoli G, Bonifati V

(2005) The G6055A (G2019S) mutation in LRRK2 is frequent in both early and late onset

Parkinson's disease and originates from a common ancestor. J Med Genet 42: e65.

42. Gubellini P, Picconi B, Bari M, Battista N, Calabresi P, Centonze D, Bernardi G, Finazzi-

Agro A, Maccarrone M (2002) Experimental parkinsonism alters endocannabinoid

degradation: implications for striatal glutamatergic transmission. J Neurosci 22: 6900-6907.

43. Guo L, Wang W, Chen SG (2006) Leucine-rich repeat kinase 2: relevance to Parkinson's

disease. Int J Biochem Cell Biol 38: 1469-1475.

44. Hallett PJ, Dunah AW, Ravenscroft P, Zhou S, Bezard E, Crossman AR, Brotchie JM,

Standaert DG (2005) Alterations of striatal NMDA receptor subunits associated with the

development of dyskinesia in the MPTP-lesioned primate model of Parkinson's disease.

Neuropharmacology 48: 503-516.

45. Healy DG, Wood NW, Schapira AH (2008) Test for LRRK2 mutations in patients with

Parkinson's disease. Pract Neurol 8: 381-385.

46. Healy DG, Abou-Sleiman PM, Valente EM, Gilks WP, Bhatia K, Quinn N, Lees AJ, Wood

NW (2004) DJ-1 mutations in Parkinson's disease. J Neurol Neurosurg Psychiatry 75: 144-

145.

47. Higashi S, Moore DJ, Colebrooke RE, Biskup S, Dawson VL, Arai H, Dawson TM, Emson

PC (2007a) Expression and localization of Parkinson's disease-associated leucine-rich repeat

kinase 2 in the mouse brain. J Neurochem 100: 368-381.

20

48. Higashi S, Biskup S, West AB, Trinkaus D, Dawson VL, Faull RL, Waldvogel HJ, Arai H,

Dawson TM, Moore DJ, Emson PC (2007b) Localization of Parkinson's disease-associated

LRRK2 in normal and pathological human brain. Brain Res 1155: 208-219.

49. Imai Y, Gehrke S, Wang HQ, Takahashi R, Hasegawa K, Oota E, Lu B (2008)

Phosphorylation of 4E-BP by LRRK2 affects the maintenance of dopaminergic neurons in

Drosophila. Embo J 27: 2432-2443.

50. Jaleel M, Nichols RJ, Deak M, Campbell DG, Gillardon F, Knebel A, Alessi DR (2007)

LRRK2 phosphorylates moesin at threonine-558: characterization of how Parkinson's

disease mutants affect kinase activity. Biochem J 405: 307-317.

51. Jankovic J (2008) Parkinson's disease: clinical features and diagnosis. J Neurol Neurosurg

Psychiatry 79: 368-376.

52. Jenner P, Marsden CD (1986) The actions of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine

in animals as a model of Parkinson's disease. J Neural Transm Suppl 20: 11-39.

53. Kehagia AA, Barker RA, Robbins TW (2010) Neuropsychological and clinical

heterogeneity of cognitive impairment and dementia in patients with Parkinson's disease.

Lancet Neurol 9: 1200-1213.

54. Kennedy MB (2000) Signal-processing machines at the postsynaptic density. Science 290:

750-754.

55. Kim E, Sheng M (2004) PDZ domain proteins of synapses. Nat Rev Neurosci 5: 771-781.

56. Kitada T, Pisani A, Porter DR, Yamaguchi H, Tscherter A, Martella G, Bonsi P, Zhang C,

Pothos EN, Shen J (2007) Impaired dopamine release and synaptic plasticity in the striatum

of PINK1-deficient mice. Proc Natl Acad Sci U S A 104: 11441-11446.

57. Kurz A, Double KL, Lastres-Becker I, Tozzi A, Tantucci M, Bockhart V, Bonin M, Garcia-

Arencibia M, Nuber S, Schlaudraff F, Liss B, Fernandez-Ruiz J, Gerlach M, Wullner U,

Luddens H, Calabresi P, Auburger G, Gispert S (2010) A53T-alpha-synuclein

overexpression impairs dopamine signaling and striatal synaptic plasticity in old mice. PLoS

One 5: e11464.

58. Lai SK, Tse YC, Yang MS, Wong CK, Chan YS, Yung KK (2003) Gene expression of

glutamate receptors GluR1 and NR1 is differentially modulated in striatal neurons in rats

after 6-hydroxydopamine lesion. Neurochem Int 43: 639-653.

59. Lang AE, Lozano AM (1998a) Parkinson's disease. Second of two parts. N Engl J Med 339:

1130-1143.

60. Lang AE, Lozano AM (1998b) Parkinson's disease. First of two parts. N Engl J Med 339:

1044-1053.

21

61. Lavedan C (1998) The synuclein family. Genome Res 8: 871-880.

62. Le WD, Xu P, Jankovic J, Jiang H, Appel SH, Smith RG, Vassilatis DK (2003) Mutations in

NR4A2 associated with familial Parkinson disease. Nat Genet 33: 85-89.

63. Lee CY, Lee CH, Shih CC, Liou HH (2008) Paraquat inhibits postsynaptic AMPA receptors

on dopaminergic neurons in the substantia nigra pars compacta. Biochem Pharmacol 76:

1155-1164.

64. Leroy E, Boyer R, Auburger G, Leube B, Ulm G, Mezey E, Harta G, Brownstein MJ,

Jonnalagada S, Chernova T, Dehejia A, Lavedan C, Gasser T, Steinbach PJ, Wilkinson KD,

Polymeropoulos MH (1998) The ubiquitin pathway in Parkinson's disease. Nature 395: 451-

452.

65. Lesage S, Leutenegger AL, Ibanez P, Janin S, Lohmann E, Durr A, Brice A (2005) LRRK2

haplotype analyses in European and North African families with Parkinson disease: a

common founder for the G2019S mutation dating from the 13th century. Am J Hum Genet

77: 330-332.

66. Li X, Patel JC, Wang J, Avshalumov MV, Nicholson C, Buxbaum JD, Elder GA, Rice ME,

Yue Z (2010) Enhanced striatal dopamine transmission and motor performance with

LRRK2 overexpression in mice is eliminated by familial Parkinson's disease mutation

G2019S. J Neurosci 30: 1788-1797.

67. Li Y, Liu W, Oo TF, Wang L, Tang Y, Jackson-Lewis V, Zhou C, Geghman K, Bogdanov

M, Przedborski S, Beal MF, Burke RE, Li C (2009) Mutant LRRK2(R1441G) BAC

transgenic mice recapitulate cardinal features of Parkinson's disease. Nat Neurosci 12: 826-

828.

68. Lin X, Parisiadou L, Gu XL, Wang L, Shim H, Sun L, Xie C, Long CX, Yang WJ, Ding J,

Chen ZZ, Gallant PE, Tao-Cheng JH, Rudow G, Troncoso JC, Liu Z, Li Z, Cai H (2009)

Leucine-rich repeat kinase 2 regulates the progression of neuropathology induced by

Parkinson's-disease-related mutant alpha-synuclein. Neuron 64: 807-827.

69. Lovinger DM, Tyler EC, Merritt A (1993) Short- and long-term synaptic depression in rat

neostriatum. J Neurophysiol 70: 1937-1949.

70. Mahon S, Deniau JM, Charpier S (2004) Corticostriatal plasticity: life after the depression.

Trends Neurosci 27: 460-467.

71. Malenka RC, Bear MF (2004) LTP and LTD: an embarrassment of riches. Neuron 44: 5-21.

72. Manning G, Whyte DB, Martinez R, Hunter T, Sudarsanam S (2002) The protein kinase

complement of the human genome. Science 298: 1912-1934.

22

73. Marin I (2006) The Parkinson disease gene LRRK2: evolutionary and structural insights.

Mol Biol Evol 23: 2423-2433.

74. Marx FP, Holzmann C, Strauss KM, Li L, Eberhardt O, Gerhardt E, Cookson MR,

Hernandez D, Farrer MJ, Kachergus J, Engelender S, Ross CA, Berger K, Schols L, Schulz

JB, Riess O, Kruger R (2003) Identification and functional characterization of a novel

R621C mutation in the synphilin-1 gene in Parkinson's disease. Hum Mol Genet 12: 1223-

1231.

75. Mata IF, Kachergus JM, Taylor JP, Lincoln S, Aasly J, Lynch T, Hulihan MM, Cobb SA,

Wu RM, Lu CS, Lahoz C, Wszolek ZK, Farrer MJ (2005) Lrrk2 pathogenic substitutions in

Parkinson's disease. Neurogenetics 6: 171-177.

76. Meixner A, Boldt K, Van Troys M, Askenazi M, Gloeckner CJ, Bauer M, Marto JA, Ampe

C, Kinkl N, Ueffing M (2010) A QUICK screen for Lrrk2 interaction partners--leucine-rich

repeat kinase 2 is involved in actin cytoskeleton dynamics. Mol Cell Proteomics 10: M110

001172.

77. Melrose H, Lincoln S, Tyndall G, Dickson D, Farrer M (2006) Anatomical localization of

leucine-rich repeat kinase 2 in mouse brain. Neuroscience 139: 791-794.

78. Moore DJ (2008) The biology and pathobiology of LRRK2: implications for Parkinson's

disease. Parkinsonism Relat Disord 14 Suppl 2: S92-98.

79. Moore DJ, Dawson VL, Dawson TM (2006) Lessons from Drosophila models of DJ-1

deficiency. Sci Aging Knowledge Environ 2006: pe2.

80. Murphy DD, Rueter SM, Trojanowski JQ, Lee VM (2000) Synucleins are developmentally

expressed, and alpha-synuclein regulates the size of the presynaptic vesicular pool in

primary hippocampal neurons. J Neurosci 20: 3214-3220.

81. Nash JE, Johnston TH, Collingridge GL, Garner CC, Brotchie JM (2005) Subcellular

redistribution of the synapse-associated proteins PSD-95 and SAP97 in animal models of

Parkinson's disease and L-DOPA-induced dyskinesia. Faseb J 19: 583-585.

82. Nemani VM, Lu W, Berge V, Nakamura K, Onoa B, Lee MK, Chaudhry FA, Nicoll RA,

Edwards RH (2010) Increased expression of alpha-synuclein reduces neurotransmitter

release by inhibiting synaptic vesicle reclustering after endocytosis. Neuron 65: 66-79.

83. Nishi M, Hinds H, Lu HP, Kawata M, Hayashi Y (2001) Motoneuron-specific expression of

NR3B, a novel NMDA-type glutamate receptor subunit that works in a dominant-negative

manner. J Neurosci 21: RC185.

84. Nussbaum RL, Polymeropoulos MH (1997) Genetics of Parkinson's disease. Hum Mol

Genet 6: 1687-1691.

23

85. O'Dell TJ, Kandel ER (1994) Low-frequency stimulation erases LTP through an NMDA

receptor-mediated activation of protein phosphatases. Learn Mem 1: 129-139.

86. Oh JD, Vaughan CL, Chase TN (1999) Effect of dopamine denervation and dopamine

agonist administration on serine phosphorylation of striatal NMDA receptor subunits. Brain

Res 821: 433-442.

87. Paille V, Picconi B, Bagetta V, Ghiglieri V, Sgobio C, Di Filippo M, Viscomi MT, Giampa

C, Fusco FR, Gardoni F, Bernardi G, Greengard P, Di Luca M, Calabresi P (2010) Distinct

levels of dopamine denervation differentially alter striatal synaptic plasticity and NMDA

receptor subunit composition. J Neurosci 30: 14182-14193.

88. Paisan-Ruiz C, Nath P, Washecka N, Gibbs JR, Singleton AB (2008) Comprehensive

analysis of LRRK2 in publicly available Parkinson's disease cases and neurologically

normal controls. Hum Mutat 29: 485-490.

89. Paisan-Ruiz C, Jain S, Evans EW, Gilks WP, Simon J, van der Brug M, Lopez de Munain

A, Aparicio S, Gil AM, Khan N, Johnson J, Martinez JR, Nicholl D, Carrera IM, Pena AS,

de Silva R, Lees A, Marti-Masso JF, Perez-Tur J, Wood NW, Singleton AB (2004) Cloning

of the gene containing mutations that cause PARK8-linked Parkinson's disease. Neuron 44:

595-600.

90. Partridge JG, Tang KC, Lovinger DM (2000) Regional and postnatal heterogeneity of

activity-dependent long-term changes in synaptic efficacy in the dorsal striatum. J

Neurophysiol 84: 1422-1429.

91. Piccoli G, Condliffe SB, Bauer M, Giesert F, Boldt K, De Astis S, Meixner A, Sarioglu H,

Vogt-Weisenhorn DM, Wurst W, Gloeckner CJ, Matteoli M, Sala C, Ueffing M (2011)

LRRK2 controls synaptic vesicle storage and mobilization within the recycling pool. J

Neurosci 31: 2225-2237.

92. Picconi B, Centonze D, Hakansson K, Bernardi G, Greengard P, Fisone G, Cenci MA,

Calabresi P (2003) Loss of bidirectional striatal synaptic plasticity in L-DOPA-induced

dyskinesia. Nat Neurosci 6: 501-506.

93. Picconi B, Gardoni F, Centonze D, Mauceri D, Cenci MA, Bernardi G, Calabresi P, Di Luca

M (2004) Abnormal Ca2+-calmodulin-dependent protein kinase II function mediates

synaptic and motor deficits in experimental parkinsonism. J Neurosci 24: 5283-5291.

94. Polymeropoulos MH, Lavedan C, Leroy E, Ide SE, Dehejia A, Dutra A, Pike B, Root H,

Rubenstein J, Boyer R, Stenroos ES, Chandrasekharappa S, Athanassiadou A,

Papapetropoulos T, Johnson WG, Lazzarini AM, Duvoisin RC, Di Iorio G, Golbe LI,

24

Nussbaum RL (1997) Mutation in the alpha-synuclein gene identified in families with

Parkinson's disease. Science 276: 2045-2047.

95. Qing H, Wong W, McGeer EG, McGeer PL (2009) Lrrk2 phosphorylates alpha synuclein at

serine 129: Parkinson disease implications. Biochem Biophys Res Commun 387: 149-152.

96. Quik M, Chen L, Parameswaran N, Xie X, Langston JW, McCallum SE (2006) Chronic oral

nicotine normalizes dopaminergic function and synaptic plasticity in 1-methyl-4-phenyl-

1,2,3,6-tetrahydropyridine-lesioned primates. J Neurosci 26: 4681-4689.

97. Raju DV, Ahern TH, Shah DJ, Wright TM, Standaert DG, Hall RA, Smith Y (2008)

Differential synaptic plasticity of the corticostriatal and thalamostriatal systems in an

MPTP-treated monkey model of parkinsonism. Eur J Neurosci 27: 1647-1658.

98. Reynolds JN, Wickens JR (2000) Substantia nigra dopamine regulates synaptic plasticity

and membrane potential fluctuations in the rat neostriatum, in vivo. Neuroscience 99: 199-

203.

99. Rizo J, Rosenmund C (2008) Synaptic vesicle fusion. Nat Struct Mol Biol 15: 665-674.

100. Schulz-Schaeffer WJ (2010) The synaptic pathology of alpha-synuclein aggregation in

dementia with Lewy bodies, Parkinson's disease and Parkinson's disease dementia. Acta

Neuropathol 120: 131-143.

101. Schwarting RK, Huston JP (1996) The unilateral 6-hydroxydopamine lesion model in

behavioral brain research. Analysis of functional deficits, recovery and treatments. Prog

Neurobiol 50: 275-331.

102. Selkoe DJ (2002) Alzheimer's disease is a synaptic failure. Science 298: 789-791.

103. Shendelman S, Jonason A, Martinat C, Leete T, Abeliovich A (2004) DJ-1 is a redox-

dependent molecular chaperone that inhibits alpha-synuclein aggregate formation. PLoS

Biol 2: e362.

104. Shin N, Jeong H, Kwon J, Heo HY, Kwon JJ, Yun HJ, Kim CH, Han BS, Tong Y, Shen J,

Hatano T, Hattori N, Kim KS, Chang S, Seol W (2008) LRRK2 regulates synaptic vesicle

endocytosis. Exp Cell Res 314: 2055-2065.

105. Sidhu A, Wersinger C, Vernier P (2004) Does alpha-synuclein modulate dopaminergic

synaptic content and tone at the synapse? Faseb J 18: 637-647.

106. Silvestri L, Caputo V, Bellacchio E, Atorino L, Dallapiccola B, Valente EM, Casari G

(2005) Mitochondrial import and enzymatic activity of PINK1 mutants associated to

recessive parkinsonism. Hum Mol Genet 14: 3477-3492.

107. Simon-Sanchez J, Schulte C, Bras JM, Sharma M, Gibbs JR, Berg D, Paisan-Ruiz C,

Lichtner P, Scholz SW, Hernandez DG, Kruger R, Federoff M, Klein C, Goate A,

25

Perlmutter J, Bonin M, Nalls MA, Illig T, Gieger C, Houlden H, Steffens M, Okun MS,

Racette BA, Cookson MR, Foote KD, Fernandez HH, Traynor BJ, Schreiber S, Arepalli S,

Zonozi R, Gwinn K, van der Brug M, Lopez G, Chanock SJ, Schatzkin A, Park Y,

Hollenbeck A, Gao J, Huang X, Wood NW, Lorenz D, Deuschl G, Chen H, Riess O, Hardy

JA, Singleton AB, Gasser T (2009) Genome-wide association study reveals genetic risk

underlying Parkinson's disease. Nat Genet 41: 1308-1312.

108. Singleton AB, Farrer M, Johnson J, Singleton A, Hague S, Kachergus J, Hulihan M,

Peuralinna T, Dutra A, Nussbaum R, Lincoln S, Crawley A, Hanson M, Maraganore D,

Adler C, Cookson MR, Muenter M, Baptista M, Miller D, Blancato J, Hardy J, Gwinn-

Hardy K (2003) alpha-Synuclein locus triplication causes Parkinson's disease. Science 302:

841.

109. Smith AD, Castro SL, Zigmond MJ (2002) Stress-induced Parkinson's disease: a working

hypothesis. Physiol Behav 77: 527-531.

110. Sossi V, de la Fuente-Fernandez R, Nandhagopal R, Schulzer M, McKenzie J, Ruth TJ,

Aasly JO, Farrer MJ, Wszolek ZK, Stoessl JA (2010) Dopamine turnover increases in

asymptomatic LRRK2 mutations carriers. Mov Disord 25: 2717-2723.

111. Spillantini MG, Crowther RA, Jakes R, Hasegawa M, Goedert M (1998) alpha-Synuclein in

filamentous inclusions of Lewy bodies from Parkinson's disease and dementia with lewy

bodies. Proc Natl Acad Sci U S A 95: 6469-6473.

112. Strack S, McNeill RB, Colbran RJ (2000) Mechanism and regulation of

calcium/calmodulin-dependent protein kinase II targeting to the NR2B subunit of the N-

methyl-D-aspartate receptor. J Biol Chem 275: 23798-23806.

113. Sudhof TC, Rothman JE (2009) Membrane fusion: grappling with SNARE and SM proteins.

Science 323: 474-477.

114. Taylor JP, Mata IF, Farrer MJ (2006) LRRK2: a common pathway for parkinsonism,

pathogenesis and prevention? Trends Mol Med 12: 76-82.

115. Taymans JM, Cookson MR (2010) Mechanisms in dominant parkinsonism: The toxic

triangle of LRRK2, alpha-synuclein, and tau. Bioessays 32: 227-235.

116. Tong Y, Pisani A, Martella G, Karouani M, Yamaguchi H, Pothos EN, Shen J (2009)

R1441C mutation in LRRK2 impairs dopaminergic neurotransmission in mice. Proc Natl

Acad Sci U S A 106: 14622-14627.

117. Turner KM, Burgoyne RD, Morgan A (1999) Protein phosphorylation and the regulation of

synaptic membrane traffic. Trends Neurosci 22: 459-464.

26

118. Ulas J, Cotman CW (1996) Dopaminergic denervation of striatum results in elevated

expression of NR2A subunit. Neuroreport 7: 1789-1793.

119. Valente EM, Abou-Sleiman PM, Caputo V, Muqit MM, Harvey K, Gispert S, Ali Z, Del

Turco D, Bentivoglio AR, Healy DG, Albanese A, Nussbaum R, Gonzalez-Maldonado R,

Deller T, Salvi S, Cortelli P, Gilks WP, Latchman DS, Harvey RJ, Dallapiccola B, Auburger

G, Wood NW (2004) Hereditary early-onset Parkinson's disease caused by mutations in

PINK1. Science 304: 1158-1160.

120. Walsh JP (1993) Depression of excitatory synaptic input in rat striatal neurons. Brain Res

608: 123-128.

121. Walsh JP, Dunia R (1993) Synaptic activation of N-methyl-D-aspartate receptors induces

short-term potentiation at excitatory synapses in the striatum of the rat. Neuroscience 57:

241-248.

122. Wang Y, Chandran JS, Cai H, Mattson MP (2008) DJ-1 is essential for long-term depression

at hippocampal CA1 synapses. Neuromolecular Med 10: 40-45.

123. Whaley NR, Uitti RJ, Dickson DW, Farrer MJ, Wszolek ZK (2006) Clinical and pathologic

features of families with LRRK2-associated Parkinson's disease. J Neural Transm Suppl:

221-229.

124. Wider C, Dickson DW, Wszolek ZK (2010) Leucine-rich repeat kinase 2 gene-associated

disease: redefining genotype-phenotype correlation. Neurodegener Dis 7: 175-179.

125. Wilson MA, St Amour CV, Collins JL, Ringe D, Petsko GA (2004) The 1.8-A resolution

crystal structure of YDR533Cp from Saccharomyces cerevisiae: a member of the DJ-

1/ThiJ/PfpI superfamily. Proc Natl Acad Sci U S A 101: 1531-1536.

126. Wishart TM, Parson SH, Gillingwater TH (2006) Synaptic vulnerability in

neurodegenerative disease. J Neuropathol Exp Neurol 65: 733-739.

127. Xiong H, Wang D, Chen L, Choo YS, Ma H, Tang C, Xia K, Jiang W, Ronai Z, Zhuang X,

Zhang Z (2009) Parkin, PINK1, and DJ-1 form a ubiquitin E3 ligase complex promoting

unfolded protein degradation. J Clin Invest 119: 650-660.

128. Xiong Y, Coombes CE, Kilaru A, Li X, Gitler AD, Bowers WJ, Dawson VL, Dawson TM,

Moore DJ (2010) GTPase activity plays a key role in the pathobiology of LRRK2. PLoS

Genet 6: e1000902.

129. Yao I, Takagi H, Ageta H, Kahyo T, Sato S, Hatanaka K, Fukuda Y, Chiba T, Morone N,

Yuasa S, Inokuchi K, Ohtsuka T, Macgregor GR, Tanaka K, Setou M (2007) SCRAPPER-

dependent ubiquitination of active zone protein RIM1 regulates synaptic vesicle release.

Cell 130: 943-957.

27

130. Yu S, Ueda K, Chan P (2005) Alpha-synuclein and dopamine metabolism. Mol Neurobiol

31: 243-254.

131. Yu S, Li X, Liu G, Han J, Zhang C, Li Y, Xu S, Liu C, Gao Y, Yang H, Ueda K, Chan P

(2007) Extensive nuclear localization of alpha-synuclein in normal rat brain neurons

revealed by a novel monoclonal antibody. Neuroscience 145: 539-555.

132. Zhang L, Shimoji M, Thomas B, Moore DJ, Yu SW, Marupudi NI, Torp R, Torgner IA,

Ottersen OP, Dawson TM, Dawson VL (2005) Mitochondrial localization of the Parkinson's

disease related protein DJ-1: implications for pathogenesis. Hum Mol Genet 14: 2063-2073.

133. Zhou C, Huang Y, Shao Y, May J, Prou D, Perier C, Dauer W, Schon EA, Przedborski S

(2008) The kinase domain of mitochondrial PINK1 faces the cytoplasm. Proc Natl Acad Sci

U S A 105: 12022-12027.

134. Zigmond MJ, Hastings TG, Perez RG (2002) Increased dopamine turnover after partial loss

of dopaminergic neurons: compensation or toxicity? Parkinsonism Relat Disord 8: 389-393.

135. Zimprich A, Biskup S, Leitner P, Lichtner P, Farrer M, Lincoln S, Kachergus J, Hulihan M,

Uitti RJ, Calne DB, Stoessl AJ, Pfeiffer RF, Patenge N, Carbajal IC, Vieregge P, Asmus F,

Muller-Myhsok B, Dickson DW, Meitinger T, Strom TM, Wszolek ZK, Gasser T (2004)

Mutations in LRRK2 cause autosomal-dominant parkinsonism with pleomorphic pathology.

Neuron 44: 601-607.